Explosive operated power tool with impact and rotation

ABSTRACT

The specification discloses a power tool, particularly for inserting self-tapping screws, comprising a working element which is arranged to be impacted and rotated and means in the body to receive a metered charge of an explosive liquid fuel which when exploded produces high pressure gas which causes the operation of the working element. The liquid fuel is preferably a monofuel.

United States Patent 1111 3, 03,40

[72] inventor Peter Bruno Kahn [56] References Cited England UNITED STATES PATENTS P 2,734,488 2/1956 Wampach 173/108 [22] Sew-2571969 3,403,738 10/1968 Burkhart etalmm. 173 105 [45] Patented Sept. 7, 1971 [73] Assignees G. K. N. Screws & Fasteners Limited imary Exammer.lames A. Lepplnk w l E l d; Attorney-Barlow 8L Barlow The Plessey Company Limited llford, England {54] EXPLOSIVE OPERATED POWER TOOL WlTH IMPACT AND ROTATION 6 Claims 3Drawing Figs. ABSTRACT: The specification discloses a power tool, particularly for inserting self-tapping screws, comprising a work- [52] [1.5. CI 173/108, ing l m nt hich is arranged to be impacted and rotated and 173/134 means in the body to receive a metered charge of an explosive [51] B25d 9/10 liquid fuel which when exploded produces high pressure gas [50] 173/ l 08, which causes the operation of the working element. The liquid 1 16, 105, 134; 60/26.], 26.1 1 fuel is preferably a monofuel.

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EXPLOSWE OPERATEDPOWER TOOL WllTHlMPACT AND ROTATION BACKGROUND OF THE-INVENTION l. Field of the Invention This-invention relates to power tools. It isparticularly concerned with power hand tools, i.e. tools arranged to be hand .held but having a power driven working element. The invention has beendeveloped in connection with tools for the inser' tion of self-tapping and piercing screws into a workpiece but may alsorbeused for running arnut onto a threaded shank and then lockingthe nut by giving it an impact.

2. Description of the PriorArt ,Such power hand tools have already been proposed and manufactured to operate off compressed airwhich isrnormally available ina factory. However, due to thenormallyavailable pressuresthe application of such tools is limited, so far as they are applied to self-tapping and piercing screws, to inserting these into comparatively thin sheet metal. The pressures normally available in factory compressed air systems are insufficient to enable screws to be driven into comparatively thick sections,re.g. steel sections of a'thickness of one-eighthinch or more.

:It is an object of thepresent invention to provide a power tool which will be capable of inserting self-tapping and piercing screws into comparatively thick sections although not limited to such use.

SUMMARY OF THE INVENTION According to the invention we provide a power tool comprising a body; a working element mounted on the body for reciprocation and rotation relativethereto, an impact member slidable in the body to deliver impact tothe working element; a rotary drive member to rotate the working element; a receiver in the body to receive a charged an explosive liquid fuel; a pump for drawing a charge of such fuel from a reservoir and feeding the charge to the receiver; adjustable metering means operable to vary the size of the charge fed to the receiver; means to explode the charge in'the receiver; a drive piston slidable inthe body to rotate the rotary drive member; and directing means to direct gas produced by explosion of said charge to slide the impact member to give an impact to the working element and to slidethe drive piston to drive the rotary drive member.

By exploding an explosive charge within the body, gas can be obtained for powering the tool at a higher pressure than the normally available compressed air. The energy available will thus be capable of effecting worlc which cannot be effected with known guns using compressed air normally available in factories. Moreover by appropriate adjustment of the metering means the size of the charge can be selected to be appropriate to the work to be done.

The liquid fuel is preferably a liquid monofuel such as isopropyl nitrate.

In one arrangement, the directing means is so arranged that the gas produced by the explosion first operates one of said members and then the other of said members. Thus the impact member may be operated before the rotary drive member where a screw is to be driven, the screw being given an impact to cause it to pierce the workpiece and then rotate it to drive it into the workpiece.

In one convenient form of construction, the tool comprises two coaxial cylinders in the body, one cylinder containing the impact member which is in the form of a piston, i.e. the impact piston, and the other cylinder containing a said drive piston which is connected to one part of a screw jack which forms the rotary drive member, the other part of the screw jack being connected to the working element. Thus the gas can move the impact piston to deliver an impact to the working element and can move the drive piston to operate the screw jack and thus to rotate the working element. In this arrangement the drive piston may be prevented from rotating relative to thebody and the other part of the screw jack may be connected to the working element through a torque-limitingclutch. In one ar rangement, the one cylinder, i.e. the cylinder containing the impact piston may lie within the other cylinder which contains the drive piston.

The receiving means may comprise a breech and said means to explode the charge comprises amanually operable firing pin capable of entering the breech. The monofuel is fired by compressing the air or-gas in the breech bythe rapid movement of the firing pin which will increase both the temperature and pressure in the breech to ensure initiation of decomposition of the monofuel.

The firing pin may be held in a cocked position against a spring catch means, release of thecatch means allowing the firing pin to enter the breech and the subsequent explosion returning the firing pin to its cocked position.

The tool may be used for inserting a self-tapping and piercing screw in a workpiece and in this instance the working element comprising a screwdriver bit and the working element is given an impact either before rotation or simultaneously with rotation. if the screwdriver bit is impacted simultaneously with rotation then it is preferred that a series of impacts be delivered to the screwdriver bit.

BRIEF DESCRIPTIONOF THEDRAWING The invention will now be described in detail by way of example with reference to the accompanying drawings in which:

FIG. 1 is a side elevation, partly in section, of a first embodiment of the invention arranged for'inserting a self-tappin g and piercing screw in a workpiece; certain parts of the tool having been omitted;

FlG. 2 is a diagrammatic axial section of the pump for charging the receiving means with the monofuel; and

FIG. 2A is explanatory of the symbol employed for illustrating the check valves in FIG. 2.

Referring now to FIGS. 1, 2 :and 2A, these show a power tool arranged to be hand held for inserting a self-tapping and piercing screw in the workpiece. The tool is in the form of a gun and comprises a barrel portion 1, a handle portion 2, a monofuel reservoir 3, and a pump 4 for the monofuel. The barrel portion 1 has a first cylindrical bore or cylinder 5 formed therein, and this contains an impact member6 in the form of a piston, i.e. an impact piston, which is slidable in the cylinder 5. The impact member is urged to the left by means of a spring 7 which surrounds a stem 8 forming part ofthe impact member. The spring 7 is interposed between the impact member and an anvil 9, the latter being arranged to be engaged by the stem 8 when the latter is moved to the right as will be described. The anvil 9 is connected to a working ele ment 10 arranged to receive a screwdriver bit, not shown and an impact delivered to the anvil 9 from the impact member 6 is transmitted to the working element 110.

The impact member is provided with an annular flange 6a which is arranged to enter a dashpot 11 to absorb the momentum of the impact member 6 should it inadvertently be caused to move to the right while the anvil 9 is in a position in which it would not be engaged by the stem 8.

The working element 10 is connected via a torque-limiting clutch 12 to one part 113 of a circulating-ball jack device, the part 13 being rotatable in bearings one of which is indicated at 13a adjacent to the dashpot 11. The left-hand portion of the part 113 is surrounded by a member 40 which is secured to the barrel portion 1.

The other part of the screw jack device comprises a drive piston 14 having a piston head 14a is which is a sliding fit in a bore in the barrel 1, the bores 15 and 5 being coaxial. The piston head Ma annular and slides between the bore 15 and the fixed member 44). A splined connection 16 is provided between the piston Hi and the barrel to prevent rotation of the piston M while allowing the latter to move longitudinally. It will be apparent that as the piston M moves longitudinally from the position shown it will cause rotation of the part 13 and thus rotation of the working element through the torque-limiting clutch 12.

At the left-hand end of the barrel portion 1 there is receiving means for a liquid monofuel comprising a decomposition chamber 17 which is connected to the cylindrical bore 5 through a breech 170. A firing pin 18 projects into the chamber 17 and is held in a cocked position shown against the action of a spring 19 by means of a self-resetting catch means 21 which can be released by a first trigger, 20. When the firing pin 18 is released it is arranged to enter the breech 17a.

When the impact member 6 is at the left-hand end of its stroke, a projection 6b thereon closes the right-hand end of the breech. As will be described below, when the breech is thus closed, release of the firing pin 18 will cause decomposition of the monofuel in the breech 17a and in the chamber 17 thus causing an explosion and at the same time resetting the firing pin 18 in its cocked position as shown.

A plate valve 22 controls the flow of gas from the cylinder 5 to the cylinder such flow being able to take place by means of a groove 5a in the wall of the cylinder 5.

The reservoir 3 can be filled with the liquid monofuel through a filler plug 41 and the pump 4 is so constructed that each stroke thereof will deliver a charge of the monofuel to the chamber 17 and the breech 17a.

The pump 4 comprises a cylinder 25 in which is slidable a piston 26 secured to a graduated piston rod 23, the latter having an operating knob 24 at its free end. A spring 27 tends to move the piston 26 to its fully withdrawn position as shown in FIG. 2 up to a stop 42. The cylinder 25 has three longitudinally spaced ports, 28, 29 and 30 and the piston 26 has a longitudinal passage 31 having three transverse branches 32, 33 and 34. In the fully withdrawn position shown the branch 32 communicates with the port 28 via the annular space between the piston rod 23 and the piston 25. The port 28 communicates through a nonreturn valve 35 with the reservoir 3. The convention used for the nonreturn valve is shown in FIG. 2A.

The transverse branch 33 in the piston 26 communicates with a longitudinal groove 36 in the piston and through this groove with the port 29. The port 29 communicates via a nonreturn valve 37 with the breech 17a and the decomposition chamber 17. Means, not shown, is provided for proportioning the amount of fuel delivered between the breech 17a and the chamber 17.

The transverse branch 34 communicates with the port 30 which is connected to atmosphere.

A set screw 38 as shown in FIG. 1 is adjustably screwed into the body of the pump 4 and limits the inward movement of the piston rod 23 and thus the piston 26 by engaging the operating knob 24. The pump is operated by depressing the knob 24 and when this occurs the piston will move to the right in FIG. 2 against the spring 27 to the extent determined by the setting of the screw 38. When this movement begins, the transverse branch 34 of the passage 31 moves out of alignment with the atmospheric vent port 30 so that continued movement of the piston to the right will draw monofuel from the reservoir 3 past the nonreturn valve 35 and through the port 28 into the annular space between the piston rod 23 and the cylinder 25. At the end of the inward movement of the piston the knob 24 is released and the spring 27 will return the piston 26 to its illustrated position. Liquid will thus be forced from the annular chamber surrounding the piston rod 23, through the branch 32, the passage 31, the branch 33, the groove 36, the port 29 and the nonreturn valve 37 into the breech 17a and the decomposition chamber 17, the apportionment being obtained as described above. At the end of the return stroke of the piston 26, the branch 34 again becomes aligned with the atmospheric vent port 30 thus preventing any buildup in the monofuel reservoir 3 via the port 28 in the case of any leakage from the decomposition chamber 17. If desired, a nonreturn valve may be incorporated into the passage 31 to act as an additional safeguard in case the port 30 should become partly blocked or should not be fully uncovered when the piston 26 reaches its fully withdrawn position.

The operation of the tool will now be described. Assuming that the impact member 6 is at the left-hand end of its stroke, the projection 61; will close the breech 17a. The pump 4 will now be operated as described above to deliver monofuel from the reservoir 3 to the chamber 17 and the breech 17a. The amount of fuel delivered by the pump will depend on the setting of the set screw 38 and the heavier the work to be done and the greater the pressure required the more fuel will be delivered. Some of the fuel will be delivered to the breech 17a and some to the decomposition chamber 17, the apportionment being obtained by means not shown. The first trigger 20 may now be operated to release the catch means 21 and thus to release the firing pin 18 so that the latter enters the breech 17a. The gas trapped in the breech will be subjected to high compression so that its temperature will rise and the monofuel in the breech will begin to decompose and will explode and the decomposition of the initial amount of monofuel in the breech 17a will initiate decomposition of the monofuel in the decomposition chamber 17. The high pressure gas produced by this decomposition will have two effects. Firstly, it will move the firing pin to the left to the position shown so that the firing pin will again return to its cocked position where it will be held by the catch means 21. The high pressure gas will also move the impact member to the right thus allowing the gas to flow from the decomposition chamber and the breech through the breech 17a into the first cylinder 5. As a result, the impact member will be forced at increasing speed to the right and will compress the spring 7 so that the stem 8 delivers an impact to the anvil 9 the impact being transferred by the anvil to the working element 10. Assuming that the working element has been furnished with a self-tapping and piercing screw the impact will cause the screw to piece the workpiece. The gas will now be in the first cylinder 5 and can then be caused to rotate the working element 10. This is effected by opening the valve 22 by means of the second trigger 22a. The gas flows along the groove 5:: bypassing the impact member 6 and flows through the valve 22 into the second cylinder 15. As a result, the piston 14 is moved to the right and is prevented from rotating relative to the barrel portion 1 by means of the splined connection 16. As a result, movement of the piston 14 to the right will cause rotation of the part 13 of the screw jack and thus rotation of the working element 10 through the torque-limiting clutch 12. A vent, not shown, is provided for allowing the gas to leave the cylinder 15 after having moved the piston 14. The piston 14 then returns to its initial position shown and the tool is ready for a further operation which is initiated by delivering a charge of the monofuel from the reservoir 3 to the decomposition chamber 17 and the breech 17a by the pump 4.

The preferred monofuel is isopropylnitrate but initiation of the explosion could be started by means other than the detonation method described hereinbefore, for example the explosion could be started by means of a spark.

Various modifications could be made to the embodiments described in which impact of the working element is effected before rotation. If desired the gases from the explosion could be fed to cause rotation of the working element, first, followed by impact. This arrangement could be used for running nuts and the impact element would be in the form to engage a nut.

If desired a single explosion could cause simultaneous impact and rotation and the impact could be in the form of a series of discrete impacts caused during rotation of the working element.

1 claim:

1. A power tool comprising a body, a working element mounted on the body for reciprocation and rotation relative thereto, an impact member slidable in the body to deliver impacts to the working element, a rotary drive member to rotate the working element, a receiver in the body to receive a charge of an explosive liquid fuel, a pump for drawing a charge of such fuel from a reservoir and feeding the charge to the receiver, adjustable metering means operable to vary the size of the charge fed to the receiver, means to explode the charge in the receiver, a drive piston slidable in the body to rotate the rotary drive member, and directing means to direct gas produced by explosion of said charge to slide the impact member to give an impact to the working element and to slide the drive piston to drive the rotary drive member.

2. A power tool according to claim 1 comprising two coaxial cylinders in the body, one cylinder containing the impact member which is in the form ofa piston and the other cylinder containing said drive piston which is connected to one part of a screw jack which forms the rotary drive member, the other part of the screw jack being connected to the working ele ment.

3. A power tool according to claim 2 wherein said other cylinder and the drive piston which it contains are annular in 

1. A power tool comprising a body, a working element mounted on the body for reciprocation and rotation relative thereto, an impact member slidable in the body to deliver impacts to the working element, a rotary drive member to rotate the working element, a receiver in the body to receive a charge of an explosive liquid fuel, a pump for drawing a charge of such fuel from a reservoir and feeding the charge to the receiver, adjustable metering means operable to vary the size of the charge fed to the receiver, means to explode the charge in the receiver, a drive piston slidable in the body to rotate the rotary drive member, and directing means to direct gas produced by explosion of said charge to slide the impact member to give an impact to the working element and to slide the drive piston to drive the rotary drive member.
 2. A power tool according to claim 1 comprising two coaxial cylinders in the body, one cylinder containing the impact member which is in the form of a piston and the other cylinder containing said drive piston which is connected to one part of a screw jack which forms the rotary drive member, the other part of the screw jack being connected to the working element.
 3. A power tool according to claim 2 wherein said other cylinder and the drive piston which it contains are annular in cross section with the impact member located within the annulus of said other cylinder.
 4. A power tool according to claim 2 wherein said drive piston is prevented from rotating relative to the body and the other part of the screw jack is connected to the working element through a torque-limiting clutch.
 5. A power tool according to claim 2 wherein said one cylinder lies within said other cylinder.
 6. A power tool according to claim 1 wherein said receiving means comprises a breech and said means to explode the charge comprises a manually operable firing pin. 